In the casting of metals, bottom pour vessels have long presented leakage problems; particularly so when the metal is molten cast iron which has been treated to form modular iron upon solidification. Such molten has a strong tendency to precipitate solid matter especially in the cooler regions in the area of a bottom pour stopper and tap hole. Any debris lodged between the engaging surfaces of the stopper and tap hole will cause leaks, poor control of the amount of metal discharged and a considerable waste of molten metal. These problems necessitate the frequent cleaning of the tap hole area which is an expensive maintenance operation.
Several techniques have been tried to solve this problem. For example, bottom pour stopper elements have been equipped with heating means to prevent formation of cool spots which promote the undesired precipitation. In addition, rotating stopper elements which simply rotate about their axis to clean the sealing surfaces have also been employed. However, these techniques have not proved entirely successful in eliminating the leakage problems.
This invention is directed toward a more accurate pouring and more maintenance-free bottom pour stopper apparatus for use in a vessel adapted to hold molten metal. The stopper apparatus comprises a rigid cylindrical stopper which controls the flow of molten metal from the vessel through a tap hole located in the bottom. Accordingly, it is an object of this invention to provide a bottom pour stopper apparatus in wich the stopper is inclined to the axis of the tap hole of the vessel. Moreover, as the stopper is moved into its tap hole closing position it is revolved and rotated by the apparatus so as to push or abrade any debris from between the sealing surfaces. More specifically, while the end of the stopper is in the tap hole, the stopper rotates about its own axis and also revolves about an axis through its lower end so that its path describes an inverted cone. These combined motions, often termed precession, provide the desired abrasive action on debris collecting in the tap hole.
The subject stopper apparatus promotes a tight seal over a long period of operation and thereby prevents leakage and provides a constant and controllable quantity of metal with each discharge operation. The precessional motion of the subject stopper apparatus will provide, among other features, a vertical component in the motion of each point on the stopper's sealing surface relative to an adjacent point on the sealing surface of the tap hole. The effect of this vertical compound is to positively remove any debris from between these surfaces. In addition, these combined motions also provide uniform wearing of the sealing surfaces, and thereby prevent the formation of grooves in these surfaces which would act as leakage paths for the molten metal. The net speed and velocity of the stopper, as provided by these combined motions, are preferably selected so that any point on the sealing surface of the stopper element will travel about at least once around the vertical axis of the tap hole while the sealing surfaces are slidably engaged, during each sealing and/or unsealing operation.